since you have a 2970 i'll recommend a gainmaster .

http://cbradiomagazine.com/Antenna%2...%20Review.html

it has a very wide usable bandwidth covering much more of the frequency range your 2970 covers than any CB antenna . if you already have a external tuner try a vector 4000 if you don't get high winds and ice . if you get pretty harsh weather the penetrator already suggested is a great antenna .